With the rising costs associated with finding, extracting and processing petroleum resources, and the ecological impact of utilizing such fuels (both real and imagined), the world is turning to alternative sources of energy. One particularly attractive source is wind. Wind is clean, economical, renewable/non-expendable and virtually available everywhere, albeit more routinely accessible in some regions than in others.
The wind-powered generators of the existing prior art tend to be large, bulky propeller-like apparatuses that of necessity must be pointed into the wind to function. This requires that a significant “footprint” be allotted to each generator, exceeding 250 feet in diameter, in some instances, as the blade rotates about its pedestal to catch the wind. In addition to being unsightly, inefficient usages of space, these propeller-like devices are a huge hazard to migratory birds. Because they slice such a huge swath through the air, unsuspecting flocks flying through/around a wind farm sporting a plurality of such devices lose a significant percentage of birds, cut down in the prime of their lives. It is estimated by some sources, based on growth rate of wind farms and current mortality rates, that between 900,000 and 1.8 million birds will lose their lives every year to these wind farms by the year 2030.
The wind generator of the present invention is significantly more efficient at capturing/converting wind energy to electricity as well as being more ecologically friendly. The wind generator of the present invention is a cylindrical turbine having pivoting vanes to increase/decrease profile on the upwind and downwind legs of the rotation. The present invention comprises a wind turbine for powering an electrical generator, the wind turbine including a) a first cylindrical drum member having a first footprint; b) a first ring at a first end of the cylindrical drum member; c) a second ring at a second opposite end of the cylindrical drum member; d) a plurality of turbine vanes extending between the first and second vanes, each of the plurality of turbine vanes have an arcuate surface for scooping the wind; e) a centrally located shaft which rotationally mounts the drum member for rotation about an axis; f) means for mounting said centrally located shaft enabling said cylindrical drum member to rotate about its longitudinal axis. In one preferred embodiment, the means mounting said drum comprises a tower which has a second footprint smaller than the first footprint of the cylindrical drum member. In this first embodiment, the shaft rotationally mounting the cylindrical drum member extends vertically and the cylindrical drum member rotates about a vertical axis.
The vanes are pivotally mounted to the first and second ring to enable them to maximize a surface exposure to wind facilitating rotation of the cylindrical drum member while minimizing surface exposure to wind opposing that rotation. Preferably, a housing surrounds the cylindrical drum member, and shutter means controls exposure of the turbine vanes to the wind, the shutter means being movably mounted on the housing, and mechanical means are provided to open and close the shutter means. In one embodiment, a low pressure outlet is positioned in the housing above the cylindrical drum member. It is feasible, and in some cases, desirable, to mount a second cylindrical drum member on the tower at a position below the first cylindrical drum member. In an alternate embodiment, the shall rotationally mounting the cylindrical drum member extends horizontally and the cylindrical drum member rotates about a horizontal axis. Applications in which the turbine of the present invention has applicability include cruise/cargo ships, offshore platforms, small aircraft for emergency power requirements, in addition to the conventional wind power farms.
The wind turbine of the present invention is most preferably mounted above the ground to position it above trees, buildings and other obstructions. In designing the turbine assembly, the desired level of useful work will be considered in sizing the assembly. The amount of working torque produced by each blade is a function of a) the area of the turbine blade exposed to normal wind velocity, b) location of the center of pressure of the turbine blade, c) the working coefficient of drag on the blade, and d) the distance the center of pressure is located from the center of rotation (i.e., the length of the moment arm). The work produced by the assembly will then be the sum of the work produced by each of the individual blades exposed to the relative wind velocity. It will be apparent that the closer the centers of pressure are to the peripheral surface of the cylindrical drum mounting them (i.e., the longer the moment arm), the greater the amount of useful work which can be extracted from the wind by each blade.
From the study of fluid dynamics, it is known that a fluid flowing against and around an orthogonally positioned object will be compressed increasing the fluid pressure, and then the fluid will accelerate around the impinging structure. As the wind flows around the cylindrical obstruction of the wind turbine of the present invention, the pressure increase occurs on the windward (front) side of the turbine. As the pressurized wind then flows around the turbine, its velocity increases pushing the vanes with it. Subsequently, as the wind transfers its energy to the vanes, it will decelerate and eventually separate from the turbine blade on the downwind side thereof. The wind will flow equally around both sides of the turbine. Accordingly, the “back side” of the turbine will be housed by a deflector shield and the vanes will pivot to limit resistance to rotation of the turbine for improved efficiency.
The amount of work performed by any turbine assembly is governed by known mathematical equations which are used in designing and constructing a turbine assembly. The assembly will be sized to extract a desired amount of work when the ambient wind velocities are at their mean value and between 50-60% of the total working area of each blade is exposed to the wind.
The governing equations areF=V×A×N×(1−Cd)
where F equals the force produced by the wind,
V is the relative wind velocity,
N is the number of turbine blades exposed at any given time, and
Cd is the coefficient of drag for each blade.T=F×R 
where T is the torque generated, and
R is the radial distance between the center of pressure of the blade and the axis of rotation.W=T×θ
where W is the work done, and
θ is the angle through which each blade rotates while engaged by the wind.
Finally the Power obtained, P=W/unit time.
In order to optimize performance, it is important that the exposure of the turbine blades be managed; that is, the vanes which are in optimal alignment with the wind direction will be exposed to the wind, while those that would resist rotation in that direction are blocked. This exposure management is accomplished by two facets of the present invention. First, the housing of the turbine assembly is equipped with shutters that can be adjusted between fully open and fully closed positions. Preferably, these shutters pivot about a horizontal axis and move upwardly and downwardly, although alternative configurations can be embodied without departing from the spirit of the invention. A limited number of shutters will be open and any given time; most preferably, the shutters which extend between a point just beyond the point of direct impact from the wind to a point 160° around the housing in the direction of the rotation of the turbine will be open to enable the turbine blades to catch the wind and convert its potential energy into actual work.
As previously mentioned, the turbine assembly will be sized to produce the needed power output to drive a generator, for example, under average wind conditions with the shutters 50% open. If wind velocity ebbs, the shutters can be opened wider to expose a greater length of each turbine blade. Conversely, when the wind velocity increases above the nominal average value, the shutters can be closed to reduce the turbine blade exposure. This control of rotational speed is needed to provide a substantially uniform rate of rotation. With a DC generator, this is needed to prevent physical overload of the generator or drive shafts. For an AC system, it is typical to operate at a constant alternator speed which will be accomplished by the use of variable speed motors in conjunction with the shutter system of the present invention. By managing turbine blade exposure using the shutter system of the present invention, the need for auxiliary equipment to turn the blades into the wind (as is the case for some prior art systems), is obviated. An alternative means of operating the shutters is to fully open them when the turbine blades are exposed to positive wind force and to fully close the shutters which would expose turbine blades to negative wind force. Obviously, this eliminates some of the control available with the preferred method. The ability of the shutters to fully close affords the turbine assembly the capability to shield the moving parts from gale force winds and other potential weather related damage.
Second, each of the turbine blades themselves pivot along their inner edge to provide maximum blade exposure to catch the wind on the upstream side of the device and to minimize the resistance to desired rotation by pivoting out of the way on the downstream side of the device. This maximizes the efficiency turbine assembly in converting the potential energy of the wind into useful power.
The wind turbine assembly of the present invention has a defined footprint of significantly smaller dimension than the propeller blade design currently being used. This affords it the opportunity to be mounted on high rise buildings, cruise ships, and offshore oil platforms, to name several applications for which the prior art systems are incapable of addressing. In addition, as depicted in one of the embodiments of the present invention, two or more turbine assemblies can be mounted on a single columnar supporting structure to enhance the use of space in any of these applications or on a “wind farm”.
Various other features, advantages, and characteristics of the present invention will become apparent after a reading of the following detailed description.